Re: PostgreSQL 12: Feature Highlights

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On Wed, May 22, 2019 at 12:33:10PM +1200, David Rowley wrote:
> On Wed, 22 May 2019 at 02:55, Bruce Momjian <[email protected]> wrote:
> > This brings up a few points.  First, it seems the change affects
> > partitioned tables and UNION ALL, which means it probably needs to be
> > listed in two sections.   Second, is it only parallelism paths that are
> > added?  I am not sure if people care about a node being removed,
> > especially when the might not even know we do that step, but they do
> > care if there are new optimization possibilities.
> 
> Like Amit, I think the optimizer section is fine.  Another thing that
> is affected is that you may no longer get a Materialize node in the
> plan.  Previously you might have gotten something like Merge Join ->
> Materialize -> Append -> Seq Scan, now you might just get Merge Join
> -> Seq Scan.  This is because Append / MergeAppend don't support mark
> and restore. Removing them would allow the materialize node to be
> skipped in cases where the single subpath of the Append does support
> mark and restore.

How is this patch for the item?  I put it in the Optimizer section.

-- 
  Bruce Momjian  <[email protected]>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

+ As you are, so once was I.  As I am, so you will be. +
+                      Ancient Roman grave inscription +

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diff --git a/doc/src/sgml/release-12.sgml b/doc/src/sgml/release-12.sgml
new file mode 100644
index 76abc95..aa3845f
*** a/doc/src/sgml/release-12.sgml
--- b/doc/src/sgml/release-12.sgml
*************** Author: Tom Lane <[email protected]>
*** 842,847 ****
--- 842,859 ----
        <listitem>
  <!--
  Author: Tom Lane <[email protected]>
+ 2019-03-25 [8edd0e794] Suppress Append and MergeAppend plan nodes that have a s
+ -->
+ 
+        <para>
+         Improve optimization of partition and <literal>UNION ALL</literal>
+         queries that have only a single child (David Rowley)
+        </para>
+       </listitem>
+ 
+       <listitem>
+ <!--
+ Author: Tom Lane <[email protected]>
  2018-12-13 [04fe805a1] Drop no-op CoerceToDomain nodes from expressions at plan
  -->
  

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